1. Field of the Invention
The present invention relates to a lens-fitted photographic film unit, more particularly to a lens-fitted photographic film unit with a built-in motor for automatic film winding.
2. Background Art
Low price lens-fitted photographic film units, hereinafter called simply film units, have been widely known, each of which is pre-loaded with an ISO-135 type photographic film cassette and has a simple photographic mechanism so that anyone can enjoy photography with ease. Since the film units are compact and handy, and mostly have a flash unit, the users can enjoy photography wherever and whenever they want. Since the pre-loaded photographic film is wound into a light-tight cassette shell one frame after each exposure, the user has only to forward the film unit to a photofinisher after the photographic film is completely exposed, without the need for rewinding the exposed photographic film nor removing the film cassette from the unit body.
After the film cassette to be developed and printed is removed from the unit body in a photo-lab or a retail photo-lab agency, the unit body is collected by a film unit manufacture for recycling. For example, a picture-taking unit having a taking lens, a shutter mechanism, a film winding mechanism and the like incorporated therein, and the flash unit are reused in a film unit, after passing various inspections. Not-reusable parts made from plastic resins are melted to be recycled as plastic resin materials.
While one exposed frame of the photographic film is wound into the cassette shell by rotating a spool of the cassette through a film winding wheel, a sprocket wheel whose sprockets are engaged in perforations of the photographic film makes one revolution. When the exposed frame of the photographic film has been wound into the cassette shell, a cam member rotating coaxially and together with the sprocket wheel causes a shutter actuating lever to move to a cocked position and also causes an arresting lever to arrest the shutter actuating lever in the cocked position and, simultaneously, lock the cam member. Accordingly, the next exposure is not enabled unless the film winding wheel is rotated to wind up the exposed frame. If the photographer forgets to wind up the exposed frame, the photographer may miss a desirable chance for taking a picture.
Using a motor for automatic film winding in the film unit as in a compact camera will eliminate such a problem and also facilitate photographing. In a conventional compact camera, a motor is disposed inside a take-up spool. The motor rotates the take-up spool to wind up a photographic film one frame at a time, and also drives a shaft through a gear mechanism to rotate a spool of a film cassette when rewinding the exposed film into the cassette shell. The compact camera further has a main switch for turning a power source of the camera ON and OFF, a switch which is turned ON when a shutter release is complete, and is turned OFF when the shutter is cocked. The compact camera also has a switch which is switched OFF so long as the shutter button is depressed, and is turned ON when the shutter button is not depressed. These switches are connected in series with the motor so that the motor is driven when all these switches are turned ON. Since the single motor should drive both the take-up spool and the shaft for the cassette spool in the compact camera, and it is necessary to consider voltage drop caused by contact resistance of these switches, the power source needs to supply the motor with a voltage of not less than 3 V.
Since the low price is one of the strong point of the film unit, if the film winding motor is to be incorporated into the film unit, the motor and its power source must be inexpensive. As an inexpensive power source for supplying 3 V voltage or more, two or more dry cells, e.g., size AA or A type alkali-manganin or manganin 1.5 V batteries, may be used. However, loading more than one dry cell needs to enlarge the size of the unit body and reduces its portability. This is undesirable in view of the nature of the film unit. A button cell or a lithium cell pack could minimize the unit body, but too expensive to use in the film unit. If may be possible to drive the motor by a single dry cell, but the speed of the motor and hence the film winding speed would be low, and still be lowered by the voltage drop due to contact resistance of switches.
Beside that, in order to automatically or electrically wind the photographic film one frame at a time in cooperation with the above-described conventional film winding mechanism wherein the sprocket wheel and the cam member are locked upon one-frame advance of the photographic film, the film winding motor must stop concurrently with the lock of the sprocket wheel. If the motor rotates the spool of the cassette by inertia after the lock of the sprocket wheel, the photographic film would be tensed to be biased toward the spool. When the shutter is released and thus the sprocket wheel is unlocked under this condition, the photographic film would slightly move toward the spool during the exposure, resulting in an blurred photograph.
Furthermore, since the film unit is expected to be recycled, the film winding motor must be easy to assemble and disassemble in term of production cost and efficiency and reusability. One problem in assembling and disassembling the motor is wiring or connection between the motor and the power source and switches for controlling the operation of the motor. Wiring with leads and solder takes much time and is unsuitable for disassembling and reassembling, and also contradict the compactness of the film unit.